Abstract Vocal learning in songbirds provides a useful model for studying how performance-based feedback is used by the nervous system in calibrating and maintaining motor skills, with particular relevance to human speech. Birdsong offers the advantages of a well-described and quantifiable behavior that is subserved by a discrete and extensively investigated set of brain regions. Song learning proceeds in two stages, both of which depend critically on hearing [17, 18]. First, during a period of sensory learning, young birds listen to and memorize the song of an adult 'tutor'. Then, during a period of sensorimotor learning, they use auditory feedback to gradually refine their own initially rambling vocalizations so that they progressively resemble the previously memorized tutor song. Normal song learning requires appropriate experience during a sensitive period in early development, and also relies on auditory feedback in adulthood to maintain precisely calibrated vocal output [4]. The similarities between song and speech in their reliance on auditory feedback suggest that investigations of song learning may provide more general insights into the behavioral and neural mechanisms that govern vocal-motor learning. In addition, we are especially interested in the function of an avian basal ganglia-forebrain circuit (the anterior forebrain pathway or 'AFP') in vocal learning. This circuit plays a central role in feedback-dependent song learning in juvenile and adult birds. Because the AFP can be studied mechanistically in the context of well-defined behavior it may prove to be a particularly tractable model for understanding basal ganglia function more generally. Here, we propose to use the techniques for auditory feedback manipulation that we developed under the previous grant cycle to extend our studies of how vocal behavior in songbirds is shaped by experience (aim 1), determine how the signals that drive learning are represented in the brain (Aim 2) and how they engage basal ganglia circuitry to change song (Aim 3). We will focus on the Bengalese finch, a species that exhibits general properties of vocal learning, but appears to rely particularly strongly on auditory feedback. Songbirds provide a model where the influence of performance-based feedback on a well-defined and quantifiable behavior can be understood at a mechanistic level. Such an understanding will provide basic insight into normal learning processes, with particular relevance to speech, and contribute to our ability to prevent and correct disabilities that arise from dysfunction of these processes.